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Objective-C:向NSMutableDictionary添加一个观察者,当计数达到0时,该字典将收到通知

nsmutabledictionary objective-c iphone

Joseph Tura · 技术社区 · 15 年前

例如,是否可以有一个类别通过调用原始方法来模拟remove方法,同时检查count是否为0?或者有没有更简单的方法。我试过KVO,但没用。。。

感谢您的帮助。

约瑟夫

2 回复 | 直到 15 年前

MrO 15 年前

在使用字典和其他“类簇”对象时,将它们“子类化”的最简单方法是创建一个子类并将其环绕在同一类型的现有对象上:

@interface MyNotifyingMutableDictionary:NSMutableDictionary {
    NSMutableDictionary *dict;
}

// these are the primitive methods you need to override
// they're the ones found in the NSDictionary and NSMutableDictionary
// class declarations themselves, rather than the categories in the .h.

- (NSUInteger)count;
- (id)objectForKey:(id)aKey;
- (NSEnumerator *)keyEnumerator;

- (void)removeObjectForKey:(id)aKey;
- (void)setObject:(id)anObject forKey:(id)aKey;

@end

@implementation MyNotifyingMutableDictionary 
- (id)init {
    if ((self = [super init])) {
        dict = [[NSMutableDictionary alloc] init];
    }
    return self;
}
- (NSUInteger)count {
    return [dict count];
}
- (id)objectForKey:(id)aKey {
    return [dict objectForKey:aKey];
}
- (NSEnumerator *)keyEnumerator {
    return [dict keyEnumerator];
}
- (void)removeObjectForKey:(id)aKey {
    [dict removeObjectForKey:aKey];
    [self notifyIfEmpty]; // you provide this method
}
- (void)setObject:(id)anObject forKey:(id)aKey {
    [dict setObject:anObject forKey:aKey];
}
- (void)dealloc {
    [dict release];
    [super dealloc];
}
@end

Joseph Tura 15 年前

我尝试了我的第一个类别,这似乎是有效的:

NSMutableDictionary+notificationsonempty.h

#import <Foundation/Foundation.h>

@interface NSMutableDictionary (NotifiesOnEmpty)
- (void)removeObjectForKeyNotify:(id)aKey;
- (void)removeAllObjectsNotify;
- (void)removeObjectsForKeysNotify:(NSArray *)keyArray;
- (void)notifyOnEmpty;
@end

#import "Constants.h"
#import "NSMutableDictionary+NotifiesOnEmpty.h"

@implementation NSMutableDictionary (NotifiesOnEmpty)
- (void)removeObjectForKeyNotify:(id)aKey {
    [self removeObjectForKey:aKey];
    [self notifyOnEmpty];
}

- (void)removeAllObjectsNotify {
    [self removeAllObjects];
    [self notifyOnEmpty];
}

- (void)removeObjectsForKeysNotify:(NSArray *)keyArray {
    [self removeObjectsForKeys:keyArray];
    [self notifyOnEmpty];
}

- (void)notifyOnEmpty {
    if ([self count] == 0) {
        [[NSNotificationCenter defaultCenter] postNotificationName:kNotificationDictionaryEmpty object:self];
    }
}
@end

我不知道这是否是一个优雅的解决方案,但它似乎工作正常。